By using different construction techniques it is possible to treat the walls so they absorb sound at various frequencies. The following pages deal with each of the frequency bands high, mid and low. By using these construction techniques you can dramatically change the acoustics of a room. High frequencies are the easiest to absorb and it gets harder as the frequency lowers. Most home studio enthusiasts only seem to treat the high frequencies in the room yet it is the mid and low frequencies that cause all the room problems.
If you study the treatment for the low and mid frequencies you will notice that the high frequencies are not effected by this construction and it is possible to have a room where all frequencies have a similar reverberation time which is the idea of the whole exercise.